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Troubleshooting Technique; Front Panel Troubleshooting - HP 465A Operating And Service Manual

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Model 465A
number for the assembly is silk screened on the
exterior of the circuit board to identify it.
for parts replacement and -hp- part
number information.
The etched circuit board is a plated-through
type. The electrical connection between sides of the
board is made by a layer of metal plated through the
component holes. When working on these boards,
observe the following general rules.
a. Use a low-heat (25 to 30 watts) small-tip
soldering iron, and a small diameter rosin
core solder.
b. Circuit components can be removed by
placing the soldering iron on the component
lead on either side of the board, and pulling up
on lead.
If a component is obviously damaged,
clip leads as close to components as possible
and then remove. Excessive heat can cause
the circuit and board to separate, or cause
damage to the component.
Component lead hole should be cleaned
with a toothpick or other appropriate device
before inserting new lead.
d. To replace components, shape new leads
and insert them in holes.
and add solder as required to insure a good
electrical connection.
e . Clean excess flux from the connection and
adjoining area.
This section contains procedures designed to
assist in the isolation of malfunctions. These pro­
cedures are based on a systematic analysis of the
instrument circuitry. These operations should be
Front Panel Symptoms
Line Lamp not glowing
Functions properly on 20 db
position only
Functions properly on 40 db
position only
Refer to
Reheat with iron,
Table 5-4

Front Panel Troubleshooting

Check fuse Fl, Ll, L2, SI, R28, S2 or Tl
Check R3. R4, R5, R6 and Bias Voltages
Check Bias Voltages and Ql, Q2.
undertaken only after it has been established that
the difficulty can not be eliminated by the Adjustment
and Calibration Procedures, Paragraph 5-13. An
investigation should also be made to insure that the
of conditions external to the
t.rouble is not a result
Model 465A.
5-23. Conduct a visual check of the Model 465A for
possible burned or loose components,
nections, or any other obvious conditions which
might suggest a source of trouble.
5-24. Table 5-4 contains a summary of the front­
panel symptoms that may be encountered.
be used in initial efforts to select a starting pOint
for troubleshooting operations.
5-25. Table 5-5, in conjunction with Figure 5-4,
contains procedures which may be used as a guide in
isolating malfunctions. The steps in Table 5-5 des­
cribe the normal conditions which should be encountered
during the checks (circled numbers
The checks outlined in Table 5-5 are not
designed to measure all circuit parameters, rather,
only to localize the malfunction. TherefDre, it is
quite possible that additional measurements may be
required to completely isolate the problem.
ponent values may vary slightly between instruments;
therefore, it should not be necessary to precisely
duplicate voltage values described.
5-27. The conditions discussed in Table 5-5 and
Figure 5-4 are based on the following criteria:
(1) the + side of C14 is removed from circuit,
opening the feedback loop: (2) Model 465A GAIN set to
40 db; and (3) 1 mv, 2 kc signal applied to Model
Possible Cause
Section V
Paragraphs 5-20 to 5-27
Table 5-4
loose con­
It should
) in Figure